Sunan Ibn Majah Book 20 Hadith 2539

It was narrated from Ibn`Abbas that the Messenger of Allah said:
“Whoever denies a Verse of the Qur'an, it is permissible to strike his neck (i.e., execute him) Whoever says, Lailaha illallahu wahduhu la sharika lahu, wa anna Muhammadan `abduhu wa rasuluhu (None has the right to be worshiped but Allah (Subhanahu-wa-Taala) alone, and Muhammad (Peace be upon him) is His slave and Messenger), no one has any was of harming him, unless he (does something which) deserves a legal punishment, and it is carried out on him.”